1. Technical Field
The present invention relates to an optical coupler that electrically couples one terminal and the other terminal through an optical signal and a producing method thereof. Specifically, the invention relates to an optical coupler that converts an input electric signal into the optical signal, and converts the optical signal into an output electric signal, thereby electrically coupling the input electric signal and the output electric signal while insulation between the input electric signal and the output electric signal is maintained, and a producing method thereof.
2. Related Art
The optical coupler includes a light emitting element that converts the input electric signal into the optical signal and a light receiving element that converts the optical signal into the output electric signal, and the optical coupler has a structure in which the light emitted from the light emitting element is received by the light receiving element after reflected by a reflecting surface. In the optical coupler, desirably the light emitting element and the light receiving element are brought close to each other in order to enhance coupling efficiency between the light emitting element and the light receiving element to increase a light receiving amount in the light receiving element. However, unfortunately a dielectric withstanding voltage is degraded when the light emitting element and the light receiving element are brought close to each other.
For example, Japanese Patent Publication Laid-Open No. 5-218491 discloses an optical coupler. In an optical coupler 11 disclosed in Japanese Patent Publication Laid-Open No. 5-218491, a light emitting element 15 and a light receiving element 16 are mounted on wiring patterns 13 and 14 formed on an upper surface of the heat-resistant substrate 12, respectively. A primary mold body 17 (translucent resin) with which the light emitting element 15 and the light receiving element 16 are covered is formed into an elliptical shape when viewed from a side face, an emission surface of the light emitting element 15 is disposed at a first focal point of the ellipse, and a light receiving surface of the light receiving element 16 is disposed at a second focal point. The reflecting surface is formed in an outer peripheral surface of the primary mold body 17 by depositing a high-reflectance metallic reflecting film 18 using Al, Au, or Cu. Surroundings of the metallic reflecting film 18 and primary mold body 17 are covered with a secondary mold body 19 in order to block ambient light.
According to the optical coupler 11 having the structure of FIG. 1, the light emitted from the emission surface (a first focal point) of the light emitting element 15 is collected in the light receiving surface (a second focal point) of the light receiving element 16 after reflected by the metallic reflecting film 18, so that the use efficiency of the light can be improved while a distance between the light emitting element 15 and the light receiving element 16 is maintained.
However, in the optical coupler 11, because the metallic reflecting film 18 is used as the reflecting surface, an insulating property between the light emitting element 15 and the metallic reflecting film 18 or an insulating property between the light receiving element 16 and the metallic reflecting film 18 is easy to degrade. Because the metallic reflecting film is deposited by sputtering, man-hour and material cost are increased, which easily increases cost of the optical coupler. Because an inorganic material layer (a metallic reflecting film) is formed at an interface between the primary mold body and the secondary mold body, unfortunately the interface is easily peeled off to degrade reliability of the optical coupler.